Electronic apparatus with pocket of low permittivity material to reduce electromagnetic interference

ABSTRACT

An electronics apparatus including a first substrate having a first surface and a second surface, a first switch connected to a second switch and soldered in series on the first surface of the first substrate creating a connection to allow switching between the first switch and the second switch at high frequency, an insulation having a third surface attached to the second surface of the first substrate, and a second substrate having a pocket of low permittivity located between the first switch and the second switch on a fourth surface of the insulation, the fourth surface being opposite to the third surface where the first switch and the second switch are located.

BACKGROUND

Field of the Disclosure

This application relates generally to improvements in power electronicsmodule. More particularly the present disclosure relates a direct bondcopper modified to reduce the electromagnetic interference and noise.

Description of the Related Art

Power modules of power electronics may be utilized in electric vehicles(EV) and hybrid electric vehicles (HEV) as a charger (changing AC toDC), an inverter (changing DC to AC), and/or a converter (DC to DC).

The power modules such as the charger, converter, and inverter generatean electrical noise. The electric noise caused by parasitic capacitancein the power module is one of the major sources of noise. In particular,a parasitic capacitance associated with chips of the power modules maybe a source of electrical noise. The electrical noise further propagatesthrough the power module to other components.

The electric noise generated by the chips may propagate through thepower module, and may interfere with other electronic devices of thevehicle. For example, the charger, the inverter, and the convertergenerate noise which may propagate and may interfere with other vehiclecomponents, such as auxiliary electronics and/or an electric motor.

To mitigate the noise generated by the chips, conventional power modulesmay include one or more noise filters. Typically, the noise filters canbe bulky and heavy, thereby increasing the weight and footprint of thepower module. The noise filters may occupy a significant portion of thefootprint of the power modules. As such, an improvement over currenttechnology that will allow reducing or eliminating the need for largeand bulky noise filters.

SUMMARY

According to an embodiment of the present disclosure, there is providedan electronic apparatus. The electronic apparatus including a firstsubstrate having a first surface and a second surface, a first switchconnected to a second switch and soldered in series on the first surfaceof the first substrate creating a connection to allow switching betweenthe first switch and the second switch at high frequency, an insulationhaving a third surface attached to the second surface of the firstsubstrate, and a second substrate having a pocket of low permittivitylocated between the first switch and the second switch on a fourthsurface of the insulation, the fourth surface being opposite to thethird surface where the first switch and the second switch are located.

The forgoing general description of the illustrative implementations andthe following detailed description thereof are merely exemplary aspectsof the teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate one or more embodiments and,together with the description, explain these embodiments. Theaccompanying drawings have not necessarily been drawn to scale. Anyvalues dimensions illustrated in the accompanying graphs and figures arefor illustration purposes only and may or may not represent actual orpreferred values or dimensions. Where applicable, some or all featuresmay not be illustrated to assist in the description of underlyingfeatures. In the drawings:

FIG. 1 is an exemplary circuit of power electronics according to thebackground art.

FIG. 2 illustrates a cross-section of the exemplary circuit of powerelectronics according to the background art.

FIG. 3A illustrates a first configuration of a direct bond copper of thepower electronics according to certain embodiments of the presentdisclosure.

FIG. 3B illustrates a second configuration of a direct bond copper ofthe power electronics according to certain embodiments of the presentdisclosure.

FIG. 3C illustrates a variation of the first configuration with airpocket completely enclosed by the insulation and the second substrateaccording to certain embodiments of the present disclosure.

FIG. 4 illustrates an equivalent capacitance generated due the presenceof an air pocket according to an exemplary embodiment of the presentdisclosure.

FIG. 5A is a graph illustrating the effect of the air pocket on acapacitance of the power electronics according to an embodiment of thepresent disclosure.

FIG. 5B is a graph illustrating the effect of increase in the air pocketarea on a resulting capacitance of the power electronics according to anembodiment of the present disclosure.

FIG. 6 is a graph illustrating the effect of air pocket on a noise levelof the power electronics according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

The description set forth below in connection with the appended drawingsis intended as a description of various embodiments of the disclosedsubject matter and is not necessarily intended to represent the onlyembodiment(s). In certain instances, the description includes specificdetails for the purpose of providing an understanding of the disclosedembodiment(s). However, it will be apparent to those skilled in the artthat the disclosed embodiment(s) may be practiced without those specificdetails. In some instances, well-known structures and components may beshown in block diagram form in order to avoid obscuring the concepts ofthe disclosed subject matter.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with an embodiment is included inat least one embodiment of the subject matter disclosed. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout the specification is not necessarily referringto the same embodiment. Further, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments. Further, it is intended that embodiments of the disclosedsubject matter cover modifications and variations thereof.

It must be noted that, as used in the specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the context expressly dictates otherwise. That is, unlessexpressly specified otherwise, as used herein the words “a,” “an,”“the,” and the like carry the meaning of “one or more.” Additionally, itis to be understood that terms such as “top,” “bottom,” and the likethat may be used herein merely describe points of reference and do notnecessarily limit embodiments of the present disclosure to anyparticular orientation or configuration. Furthermore, terms such as“first,” “second,” “third,” etc., merely identify one of a number ofportions, components, steps, operations, functions, and/or points ofreference as disclosed herein, and likewise do not necessarily limitembodiments of the present disclosure to any particular configuration ororientation.

FIG. 1 is an exemplary circuit of a power electronic device. The circuit100 can include a power supply 101, a first switch SW1 and a secondswitch SW2. A positive (+) of the power supply 101 can be connected to afirst drain 103 on the top surface of the first switch SW1. A negative(−) of the power supply 101 can be connected to a second source 107 ofthe second switch SW2. The first switch SW1 and the second switch SW2can be connected in series by electrically connecting a first source 102of the first switch SW1 to a second drain 108 of the second switch SW2.The connection between the first switch SW1 and the second switch SW2creates a high frequency point 105 during operation of the powerelectronics. The high frequency point 105 experiences a voltage changeat a high frequency due to switching between the first switch SW1 andthe second switch SW2 at a high frequency. The high frequency can rangefrom kilohertz to gigahertz depending on the rated power of a systememploying the power electronics. The high frequency point 105 can be asignificant source of noise and electromagnetic interference in thecircuit 100 which can transmit the noise and cause electromagneticinterference with other electric component of power electronics.

An electrical connection between different elements of the circuit 100creates several parasitic capacitances. For example, a first capacitanceC₁, a second capacitance C₂, and a third capacitance C₃ are created inthe circuit 100. The first capacitance C₁ exist between the secondsource 107 of the second switch SW2 and a substrate 120, the secondcapacitance C₂ exist between the high frequency point 105 and thesubstrate 120, and the third capacitance C₃ exist between the firstdrain 103 and the substrate 120.

FIG. 2 illustrates a cross-section of the circuit 100 of the powerelectronic device. The power electronic device 100 can include a firstsubstrate Cu1, a second substrate Cu2, and a third substrate Cu3attached on a first surface (above) an insulation 210. On a secondsurface (below) the insulation 210, a fourth substrate Cu4 can beattached. Further, the fourth substrate Cu4 can be soldered to a fifthsubstrate Cu5 via a third solder 204. The fifth substrate Cu5 candissipate the heat generated during operation of the power electronics.The substrates Cu1-Cu5 can be electric conductors made of material suchas copper, while the insulation 210 can be made of ceramic, aluminumoxide (Al₂O₃), aluminum nitride (AlN), or the like. The first switch SW1and the second switch SW2 can be soldered to the second substrate Cu2and the third substrate Cu3, respectively, on the first surface of theinsulation 210 to create the circuit 100. Typically, the switches SW1and SW2 are soldered to different substrates. However, in oneembodiment, the substrates Cu1-Cu3 can be configured differently tocreate the circuit 100. For instance, the first switch SW1 and thesecond switch SW2 can be soldered to a single substrate such as thesecond substrate Cu2 and the third substrate Cu3 can be eliminated.

The first switch SW1 can be soldered to the third substrate Cu3 via afirst solder 201, and the second switch SW2 can be soldered to thesecond substrate Cu2 via a second solder 202.

Further, the first switch SW1 and the second switch SW2 can beelectrically connected for example, in a series using bond wires. Forexample, a first bond wire 211 creates a connection between the firstswitch SW1 soldered on a third substrate Cu3 and the second substrateCu2, on which the second switch SW2 is soldered. The second switch SW2can be connected to the first substrate Cu1 by a second bond wire 213 tocomplete the circuit 100. As such, the first capacitance C₁ is createdbetween the first substrate Cu1 and the fourth substrate Cu4. The secondcapacitance C₂ is created between the second substrate Cu2 and thefourth substrate Cu4. The third capacitance C₃ is created between thethird substrate Cu3 and the fourth substrate Cu4. The first, second, andthird capacitances C₁, C₂, and C₃, respectively, include similardielectric material i.e., the insulation 210. The second capacitance C₂is associated with the high frequency point 105, as discussed earlier.

The inventors discovered that part of the power electronics (referred asdirect bond copper later in the present disclosure) around the secondcapacitance C₂ can be modified to reduce the parasitic capacitance inorder to reduce the source of the noise and electromagneticinterference. FIG. 3A illustrates a direct bond copper 300 of the powerelectronics according to certain embodiments of the present disclosure.The direct bond copper 300 (DBC 300 hereinafter) refers to a part of thepower electronics formed by the first switch SW1 and the second SW2soldered to the second substrate Cu2 on the first surface of theinsulation 210, while the second surface of the insulation 210 isattached to the fourth substrate Cu4. The DBC 300 includes a parasiticcapacitance such as the second capacitance C₂. To reduce the parasiticcapacitance, a low permittivity material such as an air pocket 301 of aheight H_(a) and a width W_(a) can be formed in the fourth substrate Cu4on the second surface of the insulation 210, i.e., a surface opposite tothe first surface, where the switches SW1 and SW2 are located. The lowpermittivity material can be any material having permittivity less thanthe surrounding substrate. The low permittivity material in solid,liquid or gaseous form. For instance, air (gaseous form) has apermittivity lower than the surrounding substrates Cu2, Cu4, solder,etc. In one embodiment, the low permittivity material can be polyimides,SiO₂, poly (aryl ethers), polynorbornene, polytetrafluoroethylene, orother polymers that are designed to have low permittivity as well asimproved thermal and mechanical properties.

The dimensions of the pocket of low permittivity material depend on thesize of the circuit 100. In one embodiment of the present disclosure,the volume of the air pocket is 3.82e-9 m3, and the ratio of air pocketarea to the total DBC area is 16.5%.

In one embodiment, the air pocket 301 can be positioned in proximity ofthe high frequency point 105 (in FIG. 1), which corresponds to an areabetween the switches SW1 and SW2 in FIG. 3A. In one embodiment, the airpocket 301 is positioned below the insulation 210 in the fourthsubstrate Cu4. The air pocket 301 can be further extended into the thirdsolder 204. In FIG. 3C, the air pocket 301 is completely enclosed by theinsulation 210 on one surface and the second substrate Cu2.Alternatively or in addition, the air pocket 301 can be extended intothe fifth substrate Cu5, in which case the air pocket 301 will becompletely enclosed by the insulation 210 on one surface and the fifthsubstrate Cu4. The air pocket 301 extends in a lateral direction (i.e.,perpendicular to the plane of paper) along the length of the fourthsubstrates Cu4 forming a channel. The air pocket 301 is not positioneddirectly beneath the first switch SW1 and the second switch SW2. The airpocket 301 may be formed into an intermediate copper layer such as thefourth substrate Cu4 and the solder 204 through an etching process. Inone embodiment, the air pocket 301 is rectangular in shape. It isunderstood that while a rectangular shape may be intended, the actualmanufactured shape may have slight deviations in practice, for instance,rounded edges, jagged edges, etc. Further, an air pocket of any othershape (e.g., ring-like, circular, semicircular, triangular, etc.) andsize can be formed. The DBC 300 having the air pocket 301 can bemanufactured using traditional etching process used to fabricateintegrated circuits. In one embodiment, more than one pocket of lowpermittivity can be formed in the circuit, as illustrate in FIG. 3B. Inaddition, each of the more than one pockets of low permittivity can befilled with different permittivity material.

FIG. 3B illustrates a second configuration of a direct bond copper ofthe power electronics according to certain embodiments of the presentdisclosure. The second configuration can include more than one pocket oflow permittivity material, such as air pockets 301 and 302. The airpockets 301 and 302 are in the vicinity of high frequency region of thecircuit and in the path of noise propagation. The pocket of lowpermittivity material causes a change in capacitance of the circuit. Forinstance, the capacitance of a node N1 can be evaluated, as illustratedin FIG. 4. The node N1 is a cross-section of the circuit having at leastone pocket of low permittivity material such as air pocket 301.

FIG. 4 illustrates an equivalent capacitance of the node N1 generateddue the presence of the air pocket 301 according to an exemplaryembodiment of the present disclosure. The node N1 includes a part of thesecond substrate Cu2, a part of the fourth substrate Cu4 having an areaA₂, the air pocket 301 having an area A_(air), and a fifth substrateCu5. The node N1 can have a total area A_(x). The total area A_(x) canbe a maximum area of the fifth substrate Cu5, or the area of the secondsubstrate Cu2. The areas A₂, A_(x) and A_(air) can be calculated in thex-y plane, as indicated in the FIG. 4. The capacitances within the nodeN1 include a capacitance C₂₁ between the second substrate Cu2 and thefourth substrate Cu4 separated by the insulator 210, a capacitance C₂₂between the second substrate Cu2 and the air pocket 301. Further, theair pocket 301 can have a capacitance C_(a), which is formed in serieswith the capacitance C₂₂. The resulting capacitance C₂ of a part of thepower electronics device that includes the air pocket 301 can be definedby the equation 1 below,

$\begin{matrix}{C_{2}^{\prime} = {C_{21} + \frac{C_{22}*C_{a}}{C_{22} + C_{a}}}} & (1)\end{matrix}$Where, the capacitance C₂₁ is substantially equal to a product of thepermittivity (i.e, ∈_(insulator)) Of the insulator 210 and the ratio ofthe area A₂ and thickness T of the insulator 210, the capacitance C₂₂ issubstantially equal to a product of the permittivity of the insulator210 and the ratio of the area A_(air) and thickness T of the insulator210, and the capacitance C_(a), which represents the capacitance acrossthe low permittivity material such as the air pocket 301, issubstantially equal to a product of the permittivity of the lowpermittivity material (e.g. for air the permittivity is ∈_(air)) and theratio of the area A_(air) and height H_(a) of the air pocket 301.

The resulting capacitance C′₂ is a function of the area of the lowpermittivity material (i.e., the area of the air pocket 301), the areaof different elements of the power electronics, as well as the thicknessT of the insulation 210 and the height of the air pocket 301. In theabsence of the air pocket 301, the second capacitance C₂ of a part ofthe power electronics device can be defined by the equation 2 below,

$\begin{matrix}{C_{2} = {ɛ_{insulator}*\frac{A_{X}}{T}}} & (2)\end{matrix}$

Typically, the capacitance C_(a) is lower than the capacitances C₁, andC₂. As such, the resulting capacitance C′₂ is lower than the secondcapacitance C₂. Thus, the air pocket 301 reduces the capacitance of thepower electronics, particularly beneath the first and second switchesSW1 and SW2, respectively.

The reduced capacitance, particularly at the high frequency point,causes a reduction in noise level and electromagnetic interference thatprorogates to connected components of the power electronics. The noiselevel can be reduced significantly enough to reduce or even omit the useof a noise filter. Noise filters are commonly used in electronicscircuits to reduce the noise generated during operation of the powerelectronics and can occupy 30% to 50% of the area of a powerelectronics. As such, by employing the DBC 300 with the air pocket 301the size and weight of the power electronics can be significantlyreduced.

FIG. 5A is a graph illustrating the effect of the air pocket 301 on acapacitance of the power electronics according to an embodiment of thepresent disclosure. In FIG. 5A, L1 indicates a change in the resultingcapacitance C′₂ as a function of a change in the area of the DBC 300, inwhich the thickness T of the insulation 210 is maintained at 1 mm andthe air pocket 301 is not present. L2 indicates a change in theequivalent capacitance C_(eq) when the air pocket 301 is present in theDBC 300. L3 indicates a change in the resulting capacitance C′₂ as afunction of the change in the area of the DBC 300, in which thethickness T of the insulation 210 is maintained at 0.3 mm and the airpocket 301 is not present. Comparing L2 and L3 shows that, when the airpocket 301 is present in the DBC 300, the resulting capacitance C′₂reduces more sharply as the area (or volume) of the air pocket 301increases relative to the area (or volume) of the DBC 300. A similareffect is observed between L2 and L3.

FIG. 5B is a graph illustrating the effect of increase in the air pocketarea on a resulting capacitance of the power electronics according to anembodiment of the present disclosure. The graph indicates that as thearea A₂ decreases (as a result of increase in the air pocket's 301 areaA_(air)), the resulting capacitance C′₂ decreases rapidly compared tothe second capacitance C₂ (i.e., capacitance when the air pocket 301 isnot present). As such, the power electronics with reduced capacitance(i.e., the resulting capacitance C′₂) causes less electromagneticinterference or noise propagation compared to a conventional powerelectronics having the second capacitance C₂. The resulting capacitanceC′₂ can decrease in a linear manner or non-linear manner depending onthe type of low permittivity material and the dimensions of the airpocket.

FIG. 6 is a graph illustrating the effect of the air pocket 301 on anoise level of the power electronics. In FIG. 6, the dotted linecorresponds to a noise level observed as the frequency changes for apower electronics with the second capacitance C₂ (i.e., when the airpocket 301 is not present). The solid line corresponds to a noise levelobserved as the frequency changes for a power electronics with theresulting capacitance C′₂ (i.e., when the air pocket 301 is present).The plots show that the peak noise reduces by a noise level NL1 (e.g.,10 dB) when the air pocket 301 is present in the DBC 300 of the powerelectronics. Further, the plots show that the noise level over theentire frequency range of power electronics that includes the air pocket301 is always lower than the noise level when an air pocket is notpresent.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the present disclosures. Indeed, the novel methods, apparatusesand systems described herein can be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods, apparatuses and systems described herein can bemade without departing from the spirit of the present disclosures. Theaccompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thepresent disclosures.

What is claimed is:
 1. An electronics apparatus comprising: a firstsubstrate including a first surface and a second surface; a first switchconnected to a second switch and soldered in series with the firstswitch on the first surface of the first substrate creating anelectrical connection to allow high frequency switching between thefirst switch and the second switch; insulation including a first surfaceattached to the second surface of the first substrate; and a secondsubstrate having a pocket of low permittivity material located betweenthe first switch and the second switch on a second surface of theinsulation, the second surface of the insulation being opposite to thefirst surface of the insulation where the first switch and the secondswitch are located.
 2. The apparatus according to claim 1, wherein thepocket of low permittivity material formed of an air pocket iscompletely enclosed by the insulation and the second substrate.
 3. Theapparatus according to claim 2, wherein the air pocket is substantiallyrectangular in shape located directly below the electrical connection.4. The apparatus according to claim 2, wherein the air pocket extendsalong the length of the second substrate.
 5. The apparatus according toclaim 2, wherein a first capacitance is formed between the firstsubstrate and the second substrate and a second capacitancecorresponding to the air pocket is formed in series with the firstcapacitance causing a reduction in an overall capacitance of theelectronics apparatus.
 6. The apparatus according to claim 1, whereinthe first substrate is made of copper.
 7. The apparatus according toclaim 1, wherein the second substrate is made of copper.
 8. Theapparatus according to claim 1, wherein the second substrate is solderedto a third substrate to transfer heat generated during operation.
 9. Theapparatus according to claim 1, wherein the insulation has uniformthickness under the first switch and the second switch.